1. Field of the Invention
The present invention relates to electric switches and, more particularly, to a press button type safety switch, which automatically trips off upon an overcurrent and, which enables the user to determine the on/off status from the outer appearance.
2. Description of the Related Art
A variety of electric switches, including seesaw switches and press button switches are known. In early days, a press button switch has only ONxe2x86x92OFF function, and cannot trip off automatically upon an overcurrent. In order to eliminate this problem, a variety of safety switches are developed. Regular safety switches are commonly of seesaw switching type.
FIGS. 1A and 1B show a seesaw switch 1 invented by the present inventor. This design of seesaw switch 1 uses a plank 11 to move a conducting plate 12 between on/off positions. When an overcurrent occurred, the conducting plate 12 automatically trips.
FIGS. 2A and 2B show a press button type safety switch according to Taiwan Patent No. 422404. This structure of press button type safety switch is comprised of a housing 21, a press button 22, and an actuating block 23. The press button 22 is connected to the actuating block 23. The actuating block 23 has a heart-like positioning groove 24 in the right sidewall. The right-sided terminal 25 has a top end connected with a bimetal 26. The bimetal 26 has a top free end terminating in a retaining portion 261 adapted to engage the heart-like retaining groove 24. When an overcurrent occurred, heat is transmitted from the right-sided terminal 25 to the bimetal 26, thereby causing the bimetal 26 to deform and to disengage the retaining portion 261 from the heat-like positioning groove 24, and at the same time the press button 22 is pushed upwards by the main spring 27 to the off position. This design is not practical in use. When the contacts 291 and 292 of the movable conducting block 29 contacted the contact 251 of the right-sided terminal 25 and the contact 281 of the intermediate terminal 28, the load of current is at the terminals 25 and 28 and the movable conducting block 29 but not directly produced at the bimetal 26. When heat produced upon an overcurrent, it is transferred from the movable conducting block 29 to the right-sided terminal 25 and then transferred from the right-sided terminal 25 to the bimetal 26. Therefore, the bimetal 26 does not trip off immediately upon an overcurrent.
FIGS. 3Axcx9c3E show an overload protective press button switch according to Taiwan patent publication no. 458362. This structure of overload protective press button switch comprises a housing 31, the housing 31 having a top opening 311 and two open chambers 313 and 314 separated by a partition plate 312, a metal contact unit 33 installed in the housing 31, a switching mechanism 35, a press button assembly 32, and a linkage 34. The linkage 34 comprises a spring member 342 supported on the partition plate 312, a press member 341 mounted on the spring member 342, and a swivel holder 344 pivoted to the housing 31. The swivel holder 344 has a guide hole 343, which receives the press member 341, and a positioning portion 345 connected to the switching mechanism 35.
When pressed the press button assembly 32, the press member 341 is forced downwards to compress the spring member 342 and to bias the swivel holder 344, thereby causing the switching mechanism 35 to switch on the metal contact unit 33. When switched on, the spring member 342 pushes the press member 341 back to the initial position. The upper part I of this overload protective press button switch is similar to the design of the aforesaid prior art press button switch. The lower part II of this overload protective press button switch is similar to the design of the aforesaid prior art seesaw switch. This design is similar to Yu""s Taiwan utility model no. 83365 (equivalent to U.S. Pat. No. 5,262,748) with the exception of the additional press button assembly 32. The swivel holder 344 is equivalent to Yu""s seesaw plank. This structure of overload protective press button switch is complicated, resulting in high manufacturing cost and inconvenience of use. When the push button assembly 32 pressed to the position shown in FIG. 3C, and the swivel holder 344 is biased leftwards, the metal contact unit 33 is switched on. When the user released the hand from the push button assembly 32, the push button assembly 32 is moved to the position shown in FIG. 3D. Viewing from the outside, it shows no difference between the position of 3B and the opposition of 3D, therefore the user cannot know xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d status of the switch when viewed from the outside. For on/off indication, a complicated indicator circuit must be installed.
The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a press button type safety switch, which enables the user to know xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d status of the switch from the outer appearance of the switch. It is another object of the present invention to provide a press button type safety switch, which automatically trips off upon an overcurrent. It is still another object of the present invention to provide a press button type safety switch, which is simple and inexpensive to manufacture. To achieve these and other objects of the present invention, the press button type safety switch comprises a housing, the housing having a top opening, spring means mounted inside the housing, at least two terminals mounted in the housing for connecting to power source, a switching mechanism, a press button mounted in the top opening of the housing and supported on the spring means for pressing by hand; and an actuating structure controlled by the press button to switch the switching mechanism between on/off positions. The actuating structure comprises two sliding tracks respectively formed of a plurality of sliding rails and arranged in parallel, and a push member pivoted to the press button at a bottom side and forming with the press button a linkage. The push member comprises two bottom push portions respectively supported on the switching mechanism for synchronous movement with the push member to move the switching mechanism between on/off position, two guide rods extended from two opposite lateral sides thereof and respectively slidably coupled to the sliding tracks for guiding movement of the push member to switch the switching mechanism between on/off positions, and a stop device provided on the inside above the bottom push portions. The switching mechanism comprises a plank disposed in contact with the bottom push portions of the push member adapted for switching the terminals between on/off positions, an overcurrent protective conducting plate adapted to automatically trip off the circuit of the terminals upon an overcurrent, and a stop device upwardly extended from the plank and adapted to hook up with the stop device of the push member when the switching mechanism switched on. The plank is linked to the overcurrent protective conducting plate, and forcible by the overcurrent protective conducting plate to change the tilting angle and to disengage the stop device from the stop device of the push member for enabling the press button to be pushed upwards by the spring means when the overcurrent protective conducting plate tripped off upon an overcurrent.